Conventional peanut and other nut butters consist of a mixture of solid nut particles, liquid oil, and flavorants, e.g. a sweetener such as sugar, high fructose corn syrup or honey, and salt. Peanut butter is made by roasting raw peanut kernels and then blanching and grinding them. The comminuted nut particles are suspended in the oil from the nut (of added oil) to form a product having a pasty and spreadable consistency. In time, however, part of the oil separates from the product and forms a separate layer on the top of the peanut butter and a rigid crumbly mass underneath. This tendency of peanut butter to separate on standing can be overcome to some extent by the use of stabilizers. Stabilizers are generally partially hydrogenated or highly hydrogenated fats and oils or other emulsifiers.
Peanut butters typically contain about 50% oil and about 50% solids. The stabilizer is usually added at a level of 0.5% to 3% by weight. Flavorants such as salt, sugar and molasses can be added to improve the flavor. Emulsifiers are usually added to reduce stickiness.
The spreadability and perceived stickiness (tendency of the peanut butter to adhere to stick to the roof of one's mouth and its resistance to breakdown during chewing) are highly sensitive to the fat content of peanut butter. The lower the fat content, the harder the product is to spread and the greater is the stickiness perception. Consequently, reduction of the fat content by 25% or more (to about 37% of the peanut butter) while maintaining acceptable texture has not been achieved.
Analysis of current (full fat) peanut butter products shows the particle size distribution of the peanut solids to be primarily two different ranges. One distribution curve is composed of particles in the range of from about 18 to about 118 microns, with the central portion of the distribution being between about 24 and 118 microns in size. The second particle size distribution range is primarily between about 3 microns and about 14 microns with the major distribution being between 5 microns and 11 microns. This distribution is bimodal, i.e., two distribution curves which overlap.
Work by Wong et al. defined fluid low fat nut butters with monodispersed PSD. See European patent application no. 0381259, published Aug. 8, 1990 and corresponding U.S. Pat. No. 5,079,027 issued Jan. 7, 1992. Their process utilized a roll milling operation to prepare the defatted peanut solids. These monodispersed solids have a particle size in which the major distribution (80% or more) of particles is a single particle size range of 18 microns or less, and preferably wherein 90% of the particles are less than 13 microns. Combining these solids with oil and additional ingredients (i.e., flavorants, stabilizers, emulsifiers) produced a fluid low fat peanut butter.
In contrast to Wong et al., the present invention defines a fluid, low fat nut butter with a bimodal PSD. Peanut butter products having a bimodal particle size distribution exhibit improved flavor compared to products having monodispersed particle size distribution. However, until now, it was not possible to achieve a combination of bimodal particle distribution and desirable fluidity for reduced fat peanut butters.
The process of the present invention utilizes novel defatted peanut solids which are combined with conventionally ground (full fat) peanuts under high shear mixing conditions. The novel defatted peanut solids are extruded or processed using a combination of milling (e.g. roll mill) and high shear mixing (e.g. Readco mixer) operations. These steps result in a reduced fat peanut butter with a significantly lower viscosity than obtained via roll milling along. Extruded defatted peanuts can also be optionally subjected to high shear mixing to further reduce the viscosity. The combination of these extruded or roll milled solids with ground, full-fat peanut paste in a high shear fluid mixing operation (i.e. colloid milling) results in the novel reduced fat peanut paste which displays a bimodal PSD. This is beneficial for several reasons, including the economic benefit from only defatting a portion of the total peanut stream required for the reduced fat product, and the peanut flavor benefit derived from same.
Furthermore, previous attempts at whipped or aerated peanut butters have generally resulted in poor appearance (large, visible bubbles) and poor stability of the aerated system, where bubbles grow or coalesce over time and/or the product will collapse or deaerate. We have not discovered that removal of oil (fat) from the system improves the stability of whipped peanut butters.
The present invention also achieves a significant improvement in aeration stability and product appearance by adding increasing levels of stabilizer tot he product. Higher levels of stabilizer are known to increase aeration stability and decrease the number and size of the bubbles in the product. However, in the past, the amount of stabilizer could not be increased without making the product too firm. Now, as a result of the reduced viscosity imparted by roll milling or extrusion, the level of stabilizer can be increased while the desired rheology of the product is maintained. Moreover, by use of certain crystal modifiers, the levels of stabilizer can be further increased in whipped products. The preferred stabilizer is a fully hydrogenated mid-fraction of palm oil which is high in PSP and PSS triglycerides.
We have further discovered that additional improvements in whipped appearance are possible by improving the process by which the gas dispersion is formed. This includes ensuring that all gas is dissolved before dispersion, by providing sufficient residence time at high pressure (usually the dispersion pressure) after introducing the gas into the product stream. Additionally, the quality of the dispersion initially formed is improved by providing as sharp a pressure drop as possible across the dispersion valve or orifice. Specifically, increasing the dispersion pressure and employing a slot-shaped dispersion orifice results in smaller and more uniform bubble sizes, and less streaking or discoloration resulting from bubble size variation in the bulk product. Static in-line mixers after dispersion have also been found to enhance bubble and color uniformity.
It is an object of the present invention to:
a. Provide a fluid, reduced fat peanut butter product with a bimodal particle size distribution (PSD). This encompasses both whipped (aerated) and nonwhipped low fat peanut butters.
b. Provide a process for producing (low viscosity) reduced fat peanut butter by extrusion roasting or by further processing (high shear mixing) defatted and roll milled peanut solids before combining with full fat peanut paste and/or oil. High shear (colloid) mixing the low fat peanut solids/paste/oil mixture results in additional viscosity reduction.
c. Provide a reduced or regular fat whipped peanut butter product with superior appearance and aeration stability. This product is formulated with the maximum level of stabilizer possible while achieving target penetration. Preferably the stabilizer is the high PSP/PSS palm oil fraction described herein. At least 90% of the bubbles in the whipped peanut butter have a diameter less than 150 microns, preferably less than 100 microns.
d. Provide a process for producing the superior whipped peanut butter. The appearance is further improved by forming finely dispersed gas bubbles by fully dissolving the nitrogen gas into the product stream under high pressure, and sharply releasing the pressure across an orifice or valve. The valve or orifice design has a significant effect upon the finished product appearance. At least 90% of the bubbles have a diameter less than 150 microns, preferably less than 100 microns.
All ingredient composition percentages given are by weight unless otherwise noted. All size distributions (particles and bubble) are by volume basis.